In Reply.—In their comments on our earlier editorial,1 Küster et al provide further valuable information that may help to resolve the issue regarding the endogenous-vs-exogenous origin of epidermal n-alkanes. They now provide biochemical data on two phenotypic subgroups of autosomal recessive ichthyosis, which do not differ in their content of n-alkanes, although the alkane content of both subsets was greater than the normal subsets. We agree with the authors that photodensitometric quantitation underestimates n-alkanes of shorter chain lengths due to the volatilization of shorter chain n-alkanes during the charring procedure. Since approximately half of scale n-alkanes will have a chain length less than or equal to C25,2 the true values for n-alkanes in both of their subgroups as well as in their normal subgroups are likely to be considerably higher. Thus, we believe that laboratories that rely solely on photodensitometry